Optical trapping is an established technique for the levitating, positioning and transporting of microscopic particles. The technique employs pressure exerted by one or several laser beams. Particles that can be manipulated by optical trapping include biological cells and cell constituents, such as chromosomes. Optical trapping is particularly important in applications such as the creation of hybrid cell lines, the separation of rare cells such as fetal cells in maternal blood, and the separation of chromosomes and chromosome fragments.
In order for optical trapping to achieve its full potential as a technique for the manipulation of biological particles, manipulation chambers are required that satisfy the following requirements:
a) they must be fully enclosed and have ports through which particle suspensions, culture media, and reagents can be introduced; PA1 b) they must have good optical quality windows through which the particles can be illuminated and observed with a microscope, and through which the laser trapping beam or beams can be introduced; PA1 c) they must have one or more small sized compartments, in which the particles can be introduced, separated, and processed, as well as channels connecting these compartments with each other and with the external ports; PA1 d) they must have large surface area and small thickness in order to facilitate heat exchange for the purpose of temperature control, small thickness to allow the use of concentrated suspensions, since the surface density of the particles settled onto the bottom window is kept low as a consequence of the small settling volume; and PA1 e) they can contain in-built electrical conductors required in certain processes such as electroporation and electrofusion.
The configuration of the chamber and its functions are disclosed in U.S. Pat. No. 5,100,627 and in Optical Trapping, Cell Manipulation, and Robotics, Buican, T. N., Neagley, D. L., Morrison, W. C. and Upham, B. D., SPIE Proceedings, vol. 1063, 1989, the subject matter of which is incorporated herein by reference as though recited herein in full. It has been disclosed in U.S. Pat. No. 5,100,627 that an optical trap of the type of the instant invention, can be provided with an optical manipulation chamber which consists of three layers. The two outer layers are two closely spaced windows lying in parallel planes. The two windows are of good optical quality. The three layers are glued together, as for example with a UV curable adhesive. It is also disclosed that the optical manipulation chamber is an essential part of the optical trapping instrument and that the characteristics of the chamber determine to a large extent the range of biological applications of the instrument.
The central section contains microscopic compartments and interconnecting channels. In accordance with the prior art the channels are either laser machined into thin, 120 .mu.m stainless steel stock, or photoetched into a photosensitive ceramic, such as the special ceramic, sold under the name Fotoceram, produced by the Corning corporation. A design of the ceramic center section is shown in FIGS. 2 and 3 of U.S. Pat. No. 5,100,627. One of the windows is a 170 .mu.m thick glass coverslip, while the other window is a 1 mm thick glass slide with holes in which the external ports are mounted. The thin window lies on the imaging side. The thick window also plays a structural role by supporting the external ports and giving rigidity to the chamber. The sandwich design provides chambers with complex internal structures and with uniform overall shape. The design also maximizes heat transfer between the chamber and its holder, thus allowing accurate temperature control and, if required, fast temperature changes. The multiple compartments of the chamber and the interconnecting channels provide a mechanism by which complex experiments can be performed. The channels are on the order of 100 microns and the order of about 500 microns. The compartments are the microscopic equivalent of test tubes between which the instrument can transfer cells and other biological particles. Furthermore, the channels connecting the compartments with the external ports allow the composition of the suspension medium in the compartments to be modified at will. Some of the compartments can be filled with air, thus isolating the main compartments of the chamber from each other. While this systems performs well, the production of the central layer represents a substantial expense, since the laser etching and photoetching processes are costly and result in a high cost for the chambers.